The invention relates to apparatus for monitoring the operation of fluid flow machines, and more particularly to improvements in apparatus for monitoring the flow of liquids in the outlets of metering pumps.
It is known to provide a metering pump with an upwardly extending outlet and to install in the outlet a non-floating actuator for a sensor which generates a presence indicating signal whenever a working stroke of the pump results in the propulsion of a metered quantity of liquid into the pump outlet whereby the actuator rises to the level or into the range of the sensor to thereupon descend to its lower end position. The sensor transmits presence indicating signals to an evaluating circuit which generates an alarm or defect signal in response to detected absence of such signals, e.g., in response to detected absence of a predetermined number (n) of successive presence indicating signals, namely in response to a predetermined number of idle or ineffective strokes of the pumping element (e.g., a piston or a membrane) in the metering pump.
Monitoring apparatus of the above outlined character are normally installed in or combined or otherwise associated with pumps which are designed to admit metered quantities of a first fluid into a body or flow of a second fluid at desired intervals and/or in desired quantities. In accordance with a presently known proposal, the monitoring apparatus monitors the movements of the non-floating actuator which rises in response to admission of a metered quantity of liquid into the outlet to thereupon descend and reassume its starting (lower end) position. Each lifting of the actuator results in the generation of a presence indicating signal which is evaluated and prevents the generation of an alarm or defect signal.
Monitoring apparatus which employ non-floating actuators for sensors serving to emit presence indicating signals operate satisfactorily when the viscosity of the conveyed liquid is sufficiently low to ensure that the actuator will invariably reassume its lower end position between successive working strokes of the pump. If the viscosity of the conveyed liquid is high, the actuator remains in raised position and causes the sensor to emit an uninterrupted presence indicating signal, i.e., the evaluating circuit generates a continuous feedback signal. If such feedback signal persists for an interval of time which is longer than that required by the pump to perform a predetermined number of successive working strokes, the evaluating circuit generates an error or alarm signal even though the operation of the metering pump is entirely satisfactory.
German Offenlegungsschrift No. 36 41 737 of Fecker et al. discloses an apparatus which monitors
the outlet of a lubricant supplying pump. The apparatus comprises a photoelectronic detector which monitors the level of a spherical actuator in the outlet and transmits signals to an evaluating circuit in order to arrest the machine which receives lubricant when the detector indicates that the actuator dwells in its lower end position while the pump is supposed to deliver lubricant. This publication does not discuss the problems which arise when the viscosity of the conveyed fluid changes. Moreover, such problems are not likely to arise when the apparatus is designed to monitor the operation of a pump which serves to convey only a lubricant or another fluid the viscosity of which is high or very high.
German Offenlegungsschrift No. 32 10 822 of Arens discloses a metering apparatus wherein a circuit receives signals from a pulse generator and generates a defect signal in response to detection of improper operation of the metering pump and/or in response to improper operation of the electronic circuit of the metering pump.
German Offenlegungsschrift No. 31 22 778 of Wiernicki (corresponding to U.S. Pat. application Ser. No. 191,055 filed Sept. 25, 1980) discloses an electromagnetic piston pump wherein the piston carries a magnet, and a Hall generator which monitors the position of the magnet. The polarity of signals which are transmitted by the Hall generator changes in response to movement of the magnet to different positions. An electronic circuit evaluates the signals from the Hall generator and energizes a solenoid which serves to move the piston between its positions.